# When an LP regulator drops out under load through a Southern California summer

An LP regulator that drops out under load takes appliances down one at a time, in order of demand. The 11 inch water column reading that proves it, the excess flow device that mimics it, and service at $285 to $2,500.

## Appliances that quit one at a time are pointing at the regulator

The complaint we hear is almost never about the regulator. It is about the furnace, or the
water heater, or the cooktop that will not hold a low flame. The owner has usually already
had one of those appliances looked at, replaced a board or a thermocouple, and watched the
same behavior return with a different appliance a month later.

That pattern is the diagnosis. A regulator is the only component every LP appliance shares.
When it can no longer hold outlet pressure while several appliances draw at once, the units
fail in order of how much pressure margin they have. The cooktop, which burns on almost
anything, keeps working. The furnace, with the highest single demand and a flame sense
circuit that expects a specific flame, drops first. The water heater locks out next. The
absorption refrigerator throws a fault nobody notices for a day.

So the useful question is not which appliance is broken. It is which appliances were running
at the same moment. If the answer is more than one, and if the failing unit works fine on
its own, stop paying for appliance parts.

## The manometer numbers that settle the argument

A two stage RV regulator has one job: take tank pressure, which varies with temperature from
well under 100 to well over 200 pounds per square inch, and deliver a steady 11 inches of
water column downstream. Eleven inches of water column is about four tenths of a pound. The
entire system is built around that number holding still.

There are two tests and both matter. Lockup is the pressure the regulator holds with no
appliance running, measured at a test port, and a healthy unit settles slightly above
working pressure and stays there without creeping. Working pressure is what it holds with
the total connected load running, and that is the test that catches a regulator which looks
fine on one burner. A unit that reads correctly at lockup and falls off under full demand is
this failure exactly, and a single burner check will never find it.

There is a third reading that gets skipped and should not. A slow creep upward at lockup
means the second stage is not seating, and over pressure is more dangerous than under
pressure because it pushes appliance orifices past the flame pattern they were designed
for. Sooting at a burner, yellow tips, and a fridge flue that keeps carboning up are all
over pressure symptoms.

## What a Southern California summer does to a nitrile diaphragm

The regulator sits in the LP compartment on the A frame or in a side bay, which on most
coaches means a black or dark box in direct sun. Inside it, the working parts are elastomer
diaphragms and seats. Elastomer is exactly the material that heat and time attack, and
compartment temperatures through a Southern California summer are far above what the
ambient reading on your phone suggests.

Five months a year of that, repeated across seasons, is what hardens a diaphragm. A hardened
diaphragm still seals at rest, which is why the unit passes a casual check, but it no longer
responds fast enough to a sudden increase in flow. The rubber pigtail hoses on either side
age on the same clock and for the same reason, and they are the part owners never think about
at all.

Then there is the seasonal trick that hides the problem. Propane vapor pressure rises sharply
with tank temperature, so a marginal first stage gets a great deal of help on a hundred degree
afternoon and very little at six in the morning when it is fifty five. Owners tell us the
furnace works all day and fails at dawn and conclude the furnace has a cold weather problem.
It does not.

## Check the excess flow device before you condemn the regulator

Every modern tank connector has a safety feature that reduces flow to a trickle if it senses
a large sudden demand, which is what a leak downstream would look like. Open a tank valve
quickly with appliances switched on and that device does exactly what it was designed to do,
and the resulting behavior is indistinguishable from a failed regulator: everything lights
weakly, the furnace will not stay up, and the water heater locks out.

Resetting it is straightforward and costs nothing. Shut every appliance off, close the tank
valve fully, wait, then reopen it slowly over several seconds before turning anything on. If
the system comes back to normal, the regulator was never the problem and neither was the
appliance.

The other cheap culprit is the vent. A regulator vent must stay clear and must point
downward so it cannot take on water, and in the San Gabriel Valley it collects dust, and
sometimes a mud dauber nest, in a single season parked outdoors. A blocked vent stops the
diaphragm from breathing and produces erratic outlet pressure that reads like a failing unit.
Look at it before spending anything.

## A regulator swap against a whole system leak down

**The straightforward version.** Replacing a two stage regulator, replacing both pigtails,
setting outlet pressure and verifying lockup and working pressure sits near the bottom of the
LP gas system service band, $285 to $2,500 across 1 to 10 hours. Add the $45 flat hazmat and
disposal charge that applies whenever LP is involved. Most coaches are in and out inside the
3 business day end of the systems window.

**When appliances were damaged first.** A system that ran over pressure or lean for a season
leaves marks. Furnace and heating repair runs $350 to $2,500 across 2 to 10 hours, cooktop,
oven and microwave repair runs $350 to $2,500, water heater repair and replacement runs $350
to $4,500, and refrigerator repair runs $400 to $4,500. Those are separate line items because
they are separate parts, and they are the real cost of leaving a regulator alone for two
years.

**When the whole system has to be proven.** A coach with a history of pressure problems, a
smell complaint, or an unknown service history gets an LP safety inspection at $285 to $700
across 1 to 3 hours, which is a documented leak down of the entire system rather than a spot
check at the regulator. On any coach that has been sitting, that is the item we would spend
money on first.

## Marshall Excelsior part numbers, pigtails and lead times

Marshall Excelsior builds a large share of the two stage and automatic changeover regulators
on North American coaches, and they are not one part. Inlet configuration, outlet size,
capacity in BTU per hour, and whether the unit is a single tank two stage or a two tank
changeover all vary. A regulator sized for a small travel trailer will drop under load on a
coach running a furnace, a water heater and a fridge together, and that mismatch is a real
cause of this failure on coaches with a previous replacement.

The good news on the calendar. Common two stage and changeover regulators, pigtails in
standard lengths, and test port adapters are stocked items and generally land inside a week.
The exceptions are high capacity units on large diesel coaches and anything with a
non standard inlet on an older or imported chassis, which run 2 to 3 weeks.

The order data is the label on the regulator body plus the total connected BTU load of your
appliances. We add those up during evaluation rather than matching the part that came off,
because matching the part that came off perpetuates an undersized installation. Special order
items carry a 100 percent deposit at order and it is non refundable.

## LP work is certification gated, and the DIY line is very short

Every part of this job that opens the gas side is certification gated and is performed by the
certified technician in the shop. That includes the regulator itself, the pigtails, the
manifold, the test port, and the leak down verification that has to follow any of them. There
is no version of this where a joint gets reassembled by feel and called good, because an LP
joint inside an occupied vehicle is not a place for optimism.

The owner side is short but genuinely useful. You may cycle the tank valve slowly to reset
the excess flow device. You may look at the vent and clear obvious debris from the outside of
it. You may note the date stamp on your pigtail hoses. You may record which appliances were
running when the failure happened, and at what outside temperature and what time of day.

What you should not do is adjust the regulator's pressure screw, remove the vent cover,
replace a pigtail, or chase a smell with soapy water and then keep using the coach. If you
smell gas, shut the tank valve, get everyone out, and do not operate anything electrical in
the compartment.

## What to do this week, and what to leave alone

Run the test that costs nothing. With the tank open and reset slowly, light the cooktop, then
add the water heater, then call for heat from the furnace, and watch each flame as the next
load comes on. If the cooktop flame drops visibly when the furnace fires, you have your answer
without a meter. Repeat it once in the afternoon and once at first light, because the
temperature difference is diagnostic.

Then note the date stamps on both pigtails and the label data off the regulator body, and add
up the BTU ratings on your appliance data plates. That is everything we need to quote the job
before the coach arrives.

We are 18.4 miles from Hacienda Heights, 24 to 38 minutes via SR-60 west to Fullerton Road,
or SR-60 to SR-57 south and SR-91 east when the corridor is stacked. All LP work happens in
the bay at the Yorba Linda facility and nowhere else. Call (949) 799-3387 with the regulator
label data and your appliance list. The RV systems estimate is $150 and it is credited to an
authorized repair.

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Source: https://ocrv.club/blog/lp-regulator-drops-out-under-load-in-a-southern-california-summer
OCRV Center, 23281 La Palma Ave, Yorba Linda, CA 92887
Phone (949) 799-3387. Email info@ocrvcenter.com.
Serving Hacienda Heights and the surrounding area. 18.4 miles, 24 to 38 minutes via SR-60 west to Fullerton Rd, then south to La Palma Ave.
In shop work only. All estimates are priced and credited against an authorized repair.